The present invention relates generally to high pressure relief valves and, more particularly, to pilot operated relief valves for use in fluid systems, both gas and liquid, to protect the system from excessive pressures. A relief valve is pre-set and, ideally, should open when the system pressure reaches a certain predetermined maximum value. This ideal valve then relieves a particular volume of fluid necessary to maintain the predetermined, maximum pressure level and then closes tightly at the instant the system pressure drops to a value below the maximum pre-set level. Unfortunately, in actual practice, this ideal is not always realized. Commonly used relief valves have a cracking or threshold pressure level, the pressure at which the valve begins to open, and a full flow pressure level, the pressure required to open them fully. The difference between full-flow pressure and cracking pressure levels is the pressure differential of the value, commonly referred to as the valve override. The smaller the pressure differential, or overide, the greater the sensitivity of the valve. Prior relief valves generally exhibit excessive differential which causes them to open at the cracking threshold at a pressure level far below the pre-set maximum system pressure level, which, greatly diminishes the useful flow in the fluid system. Prior valves are also prone to excessive chattering which is generally caused by an instability of the internal fluid sealing elements. In addition, these prior devices also exhibit an objectionable characteristic referred to as "dead band" wherein the value closes at a pressure valve which is different than the pressure at which the valve opens. Ideally, a relief valve should exhibit a zero dead band characteristic and, thus, open and close at substantially the same fluid pressure value. In addition, many prior valves also develop leakage problems, particularly, at higher system pressures, for example, above 20,000 psi.
The present invention solves these prior problems by providing a full flow pressure relief valve, suitable for very high system fluid pressures, on the order of up to 25,000 psi or greater. The present invention provides a pressure relief valve in which the valve differential override is minimized so as to yield a valve with improved performance and sensitivity at these high fluid pressures. In addition, the dead band characteristic is substantially eliminated in the present valve.
My invention further provides a pressure relief valve which eliminates the prior problem of pilot chattering by way of an improved plunger and poppet arrangement. Further, the relief valve of my invention provides improved life in hostile environments, to virtually eliminate leakage problems due to corrosion or erosion. Should maintenance be required, the pressure relief valve of the invention still further provides a composite valve body which may be refurbished at minimal cost by merely replacing the worn components. In addition, the invention provides a poppet sealing arrangement in which fluid leakage is eliminated at the aforementioned high pressure.